1.4.4 - Empirical and Molecular Formulas
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what is a molecular formula?
a chemical formula showing the actual number of atoms of each element present in a compound
What is a empirical formula?
a molecular formula expressed in its simplest ratio
How do you change a molecular formula into an empirical formula?
reduce the subscripts by finding lowest common multiple
What is the difference between molecular and empirical formulas for ionic compounds?
nothing (already reduced)
In essence, what does the empirical formula tell us?
the ratio of elements in a compound
how do you solve a problem where percentages of elements are given for a compound and you have to find the empirical formula of the compound?
• assume 100g sample and state each percentage to grams • determine # of moles of each element in 100g sample • set up a mole ratio and reduce to lowest whole # by dividing each value by the smallest of the values • state empirical formula with the whole numbers as the subscripts for each element
What do you do when finding empirical formula and you divide each value by the smallest value and one of the resulting values is close to 0.5?
multiply everything by 2
What do you do when finding empirical formula and you divide each value by the smallest value and one of the resulting values is close to 1/3?
multiply each value by 3
What is the percent composition of an element?
How much of the mass of the compound is contributed by each element
How do you find the theoretical percent compositions of elements in a compound?
find the total molar mass of the element and divide by the total molar mass of the compound, then multiply by 100%